1. Field of the Invention
The present invention relates to the control of hydraulic rolling reduction in a rolling mill, and more particularly to a method and apparatus that permit the gap between the rolls to be adjusted in accordance with the output that may be provided by comparing the actual value as measured against a specific value that is set for the gap between the rolls and determining any difference between the two values.
2. Description of the Prior Art
A hydraulic rolling reduction apparatus for the rolling mill is known. For one apparatus, it is disclosed that the rolling reduction for the rolls is controlled by using an elastic body that is interposed between a moving part in a sensor that detects the positions of the rolls and a hydraulically-operated cylinder that moves the sensor's moving part toward the moving part in the cylinder (Japan examined patent publication No. 58-23162). For another apparatus, it is disclosed that the gap between the rolls is controlled by a flow rate control loop in which the output gain from the flow rate control system can be maintained to be constant (Japan examined patent publication No. 61-13885). In this patent, the flow rate control loop includes a sensor that detects the flow rate for the hydraulic fluid, and a rate control circuit that responds to any deviation of the detection signal from a flow rate reference signal and provides an operating current reference signal for controlling the degree of opening of a servo valve. There is also an apparatus that includes an automatic leak compensation controller (Japan examined patent publication No. 59-50407). This patent discloses that the controller includes a means for setting the positions of the rolls, a means for sensing the positions of the rolls as set by the setting means, a integrator circuit that integrates any difference between the setting position and the output of the sensor means, a pulse generator, a pulse counter, a digital to analog (D/A) converter that converts the output of the pulse counter to a corresponding analog signal, a comparator that compares the output of the integrator and the output signal of the D/A converter, and a circuit means that generates an ADD pulse or SUBTRACT pulse in response to the output of the comparator to be added to the servo valve control signal.
The apparatus disclosed in the patents mentioned above are specifically designed for use in large scale applications, and have complicated mechanisms necessary to meet the requirements for those particular applications. It may be expected that each apparatus performs well in its own operating environment, but that the design is not such that it can also be used in medium or small scale applications. As such, they are not general-purpose controllers. Particularly, it is difficult for any apparatus to control the gap between the rolls with high precision (such as a precision of above 1/1000 mm) and easily, by moving a slight amount of hydraulic fluid. No apparatus that implements this conceptual architecture has yet been known.